The present invention relates to video switcher architectures, and more particularly to a layered mix effects switcher architecture that is an extension of a conventional mix effects based switcher architecture, the layered mix effects switcher architecture providing a parallel key path for each video path throughout the switcher, i.e., each video input and output has an associated key input and output.
The major functional blocks of a traditional mix effects based video switcher architecture, commonly called mix effects (M/E) banks, always output full screen video without an associated key. Key signals are only processed and used to composite video signals within the functional blocks, and are separate and limited in number with respect to the video inputs. With the advent of digital switchers the capabilities for mixing multiple layers of video signals are expanded. However the traditional mix effects based switcher architecture does not fit well into the digital compositing, or layering, world.
The traditional mix effects (M/E) based switchers implement a basic layering concept within a mix effects bank, but not between M/E banks. A conventional M/E bank has as inputs two background video sources without key and two "video with key" sources, where the keys may be developed from the video itself as "self" keys or may be external keys. The video with key sources are input to keyers in the M/E bank and are called the "fills", for the video, and the "hole-cutters", for the key. The output from the M/E bank is a full raster video signal with no key signal that represents the layering of the video signals composited with the background video according to their associated keys. To composite two character generators that are outputting some font video with associated key, the traditional switcher layers the two fonts, but also necessarily puts them over a background before M/E output.
What is desired is a mix effects based switcher architecture that can take advantage of the expanded capabilities of digital switchers by allowing an operator to turn the background off and output the composite video and an associated composite key from one M/E bank to allow re-entry into another M/E bank or output from the switcher. This allows many layers of video signals to be composited together while maintaining compatibility with traditional mix effects based switcher architectures.